Precious metal and telluride mineralogy of large volcanic-hosted massive sulfide deposits in the Urals

Summary The study focuses on the mode of occurrence of Au, Ag and Te in ores of the Gaisk, Safyanovsk, Uzelginsk and other volcanic-hosted massive sulfide (VHMS) deposits in the Russian Urals. Minerals containing these elements routinely form fine inclusions within common sulfides (pyrite, chalcopyrite and sphalerite). Gold is mostly concentrated as ‘invisible’ gold within pyrite and chalcopyrite at concentrations of 1–20 ppm. Silver mainly occurs substituted in tennantite (0.1–6 wt.% Ag). In the early stages of mineralization, gold is concentrated into solid solution within the sulfides and does not form discrete minerals. Mineral parageneses identified in the VHMS deposits that contain discrete gold- and gold-bearing minerals, including native gold, other native elements, various tellurides and tennantite, were formed only in the latest stages of mineralization. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of the common sulfides, the appearance of submicroscopic and microscopic inclusions of Au–Ag alloys (fineness 0.440–0.975) and segregation of trace elements into new, discrete minerals. The latter include Au and Ag compounds combined with Te, Se, Bi and S. Numerous tellurides (altaite, hessite, stützite, petzite, krennerite etc.) are found in the massive sulfide ores of the Urals and appear to be major carriers of gold and PGE in VHMS ores.     

Gold and sulphide minerals in Tertiary quartz pebble conglomerate gold placers, Southland, New Zealand

Auriferous quartz pebble conglomerates (QPC) formed during Tertiary sedimentary recycling in the Waimumu district, Southland, New Zealand. These sediments contain fine-grained gold of detrital origin with abundant surface textures and gold-forms associated with authigenic gold remobilisation. Most authigenic gold contains no detectable silver and occurs as overgrowths on detrital Au–Ag and Au–Ag–Hg alloys that contain up to 13 wt.% Ag, and 9 wt.% Hg. Fine-grained Au–Ag and Au–Ag–Hg alloys are compositionally heterogeneous, exhibiting both well-defined silver-depleted and silver-enriched rims. Rare coarse Au–Ag alloy is intergrown with quartz and is homogenous. Discrete grains of authigenic, porous, sheet-like gold occur in carbonaceous mudstone within a QPC sequence. Some QPC contain abundant sulphide minerals. Some of these sulphides (pyrite and arsenopyrite) are of long-distance detrital origin, presumably from the Otago Schist, whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin, derived from the erosion of QPC and underlying Tertiary sediments. There has also been authigenic deposition of sulphide minerals in the QPC themselves. These diagenetic sulphides include framboidal and anhedral marcasite, and framboidal and euhedral pyrite. Sulphur isotope data for the sulphide minerals range from − 45‰ to + 18‰ (relative to VCDT). Sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from − 9‰ to − 1‰ and are most likely derived from the Otago Schist to the north. Both framboidal and anhedral marcasite have lower values (< − 20‰) reflecting microbial sulphate reduction as a source for the precursor hydrogen sulphide. Anhedral marcasite contains elevated concentrations of Ni, Co, As and Cr, commonly with compositional banding of these metals.Both the gold and diagenetic sulphides from the Belle-Brook QPC are compositionally similar to gold and sulphides from Archaean QPC. Porous, sheet-like authigenic gold is morphologically similar to gold associated with carbonaceous material in the Witwatersrand. In addition, Southland marcasite textures resemble the rounded and banded pyrite in Witwatersrand QPC placers. There is abundant evidence from these Tertiary QPC in southern New Zealand for sedimentary transport of sulphide minerals and post-depositional sulphide mineralisation in the surficial environment despite an oxygen-rich atmosphere. These young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers. Many of these textures are similar to those commonly ascribed to metamorphic processes in Archaean auriferous QPC.     

A study on the distribution characteristics and existing states of cadmium in the Jinding Pb-Zn deposit,Yunnan Province,China

The distribution characteristics and existing state of cadmium in the Jinding Pb-Zn deposit were studied. It was discovered that Cd was mainly distributed in sphalerite as an isomorphic impurity. There was a good correla-tion between Cd and Zn in the primary ore. With the oxidation and resolution of pyrite, sphalerite, sulfide, and etc., many secondary minerals, such as colloform sphalerite and smithsonite, were formed. The distribution of Cd is not symmetrical, and enrichment and dilution were observed in partial area of the oxidation zone in the deposit. Cd, except in external pore space or cracks of secondary minerals as independent minerals, such as greenockite, was mainly distributed in sphalerite as an isomorphic impurity in the secondary sphalerate and smithsonite in the oxida-tion zone. The research showed that Cd showed a very strong active transfer ability in the oxidation process, not only indicating that supergene leaching might be the main reason for Cd enrichment in some Pb-Zn deposits, but also reflecting that Cd was easily mobilizeed and transferred to pollute ore areas in the oxidation process. Furthermore, Cd in oxidation ore was more easily mobilized and transferred to induce bad hazards for ore areas with the effect from AMD which was produced from oxidation of sulfides.     

Petrography, mineralogy and geochemistry of the Zarshuran Carlin-like gold deposit, northwest Iran

Gold mineralisation at Zarshuran, northwestern Iran, is hosted by Precambrian carbonate and black shale formations which have been intruded by a weakly mineralised granitoid. Granitoid intrusion fractured the sedimentary rocks, thereby improving conditions for hydrothermal alteration and mineralisation. Silicification is the principal hydrothermal alteration along with decalcification and argillisation. Three hydrothermal sulphide mineral assemblages have been identified: an early assemblage of pyrrhotite, pyrite and chalcopyrite; then widespread base metal sulphides, lead-sulphosalts and zoned euhedral arsenical pyrite; and finally late network arsenical pyrite, massive and colloform arsenical pyrite, colloform sphalerite, coloradoite, and arsenic–antimony–mercury–thallium-bearing sulphides including orpiment, realgar, stibnite, getchellite, cinnabar, lorandite and a Tl-mineral, probably christite. Most of the gold at Zarshuran is detectable only by quantitative electron microprobe and bulk chemical analyses. Gold occurs mainly in arsenical pyrite and colloform sphalerite as solid solution or as nanometre-sized native gold. Metallic gold is found rarely in hydrothermal quartz and orpiment. Pure microcrystalline orpiment, carbon-rich shale, silicified shale with visible pyrite grains and arsenic minerals contain the highest concentrations of gold. In many ways Zarshuran appears to be similar to the classic Carlin-type sediment-hosted disseminated gold deposits. However, relatively high concentrations of tellurium at Zarshuran, evidenced by the occurrence of coloradoite (HgTe), imply a greater magmatic contribution in the mineralising hydrothermal solutions than is typical of Carlin-type gold deposits. Received: 13 May 1999 / Accepted: 2 February 2000     

Chimneys in Paleozoic massive sulfide mounds of the Urals VMS deposits: Mineral and trace element comparison with modern black,grey, white and clear smokers

In the Urals, a wide range of well-preserved chimneys are found in VMS deposits, which are associated with ultramafic (Atlantic type: Dergamysh), mafic (Cyprus type: Buribay), bimodal mafic (Uralian type: Yubileynoye, Sultanovskoye, Yaman-Kasy, Molodezhnoye, Uzelga-4, Valentorskoye) and bimodal felsic (Kuroko or Baymak type: Oktyabrskoye, Tash-Tau, Uselga-1, Talgan, Alexandrinskoye) sequences. Chimneys have also been found in the Safyanovskoye deposit (Altay type) that is hosted by intercalated felsic lavas and carbonaceous shales. A combination of geological, mineralogical and trace element data provide a general outline for comparison between chimneys from the Urals deposits and modern vent sites. The chimneys from the Dergamysh deposit show a broad affinity with those from the Rainbow and other vent sites associated with serpentinites of the Mid-Atlantic Ridge. The chimneys from the Buribay deposit are similar to the black smokers of the EPR vent sites including the scarcity of rare minerals. The chimneys from the Urals type of the VMS deposits show some similarities with grey smokers from the Brother Volcano and PACMANUS sites. The chimneys from the Baymak type of the VMS deposits resemble grey and white smokers of the PACMANUS and grey smokers of the Suiyo vent sites. The chimneys from the Safyanovskoye deposit are similar to the black and clear smokers from the Okinawa Trough. Mineral assemblages are controlled by the combination of host rock composition and physico-chemical conditions of the ore-forming processes. Amount of colloform pyrite, isocubanite and pseudomorphic pyrite and marcasite after pyrrhotite decreases in the chimneys across the range from ultramafic and mafic to felsic-hosted deposits and is concomitant with increase in the contents of sphalerite, galena, bornite, fahlores, native gold and barite across this range. The chimneys from the Urals type contain abundant tellurides and sulfoarsenides, while these minerals are rare (except for hessite) in the Baymak type deposits. In the same range, the buffering capacity of host rocks decreases in contrast to the increase in ƒS₂ and ƒO₂. With the exception of the Safyanovskoye deposit, trace element assemblages in chalcopyrite vary to reflect the host rock: ultramafic (high Se, Sn, Co, Ni, Ag and Au) → mafic (high Co, Se, Mo and low Bi, Au and Pb) → bimodal mafic (high Te, Au, Ag, Bi, Pb, Co, moderate Se, and variable As and Sb) → bimodal felsic (high As, Sb, Mo, Pb, moderate Bi, and low Co, Te and Se). In sphalerite of the same range, the contents of Bi, Pb, Ag, Au and Sb increase versus Fe, Se and Сo. The variations in trace elements in colloform pyrite coincide with these changes. The specific mineral changes in the local ranges from Cu- to Zn-rich chimneys in each VMS deposit are similar to the general changes in the range of host rock classes of the deposits. However, the local T, ƒS₂ and ƒO₂ changes can broadly be interpreted in terms of contribution of variable oxygenated cold seawater to the subseafloor and seafloor hydrothermal processes.     

Sedimentary rock-hosted Au deposits of the Dian–Qian–Gui area, Guizhou, and Yunnan Provinces, and Guangxi District, China

Sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area in southwest China are hosted in Paleozoic and early Mesozoic sedimentary rocks along the southwest margin of the Yangtze (South China) Precambrian craton. Most deposits have characteristics similar to Carlin-type Au deposits and are spatially associated, on a regional scale, with deposits of coal, Sb, barite, As, Tl, and Hg. Sedimentary rock-hosted Au deposits are disseminated stratabound and(or) structurally controlled. The deposits have many similar characteristics, particularly mineralogy, geochemistry, host rock, and structural control. Most deposits are associated with structural domes, stratabound breccia bodies, unconformity surfaces or intense brittle–ductile deformation zones, such as the Youjiang fault system. Typical characteristics include impure carbonate rock or calcareous and carbonaceous host rock that contains disseminated pyrite, marcasite, and arsenopyrite—usually with μm-sized Au, commonly in As-rich rims of pyrite and in disseminations. Late realgar, orpiment, stibnite, and Hg minerals are spatially associated with earlier forming sulfide minerals. Minor base–metal sulfides, such as galena, sphalerite, chalcopyrite, and Pb–Sb–As–sulphosalts also are present. The rocks locally are silicified and altered to sericite–clay (illite). Rocks and(or) stream-sediment geochemical signatures typically include elevated concentrations of As, Sb, Hg, Tl, and Ba. A general lack of igneous rocks in the Dian–Qian–Gui area implies non-pluton-related, ore forming processes. Some deposits contain evidence that sources of the metal may have originated in carbonaceous parts of the sedimentary pile or other sedimentary or volcanic horizons. This genetic process may be associated with formation and mobilization of petroleum and Hg in the region and may also be related to As-, Au-, and Tl-bearing coal horizons. Many deposits also contain textures and features indicative of strong structural control by tectonic domes or shear zones and also suggest syndeformational ore deposition, possibly related to the Youjiang fault system. Several sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area also are of the red earth-type and Au grades have been concentrated and enhanced during episodes of deep weathering.     

Criteria for the detection of hydrothermal ecosystem faunas in ores of massive sulfide deposits in the Urals

The ore-formational, ore-facies, lithological, and mineralogical-geochemical criteria are defined for the detection of hydrothermal ecosystem fauna in ores of the volcanic-hosted massive sulfide deposits in the Urals. Abundant mineralized microfauna is found mainly in massive sulfide mounds formed in the jasperous basalt (Buribai, Priorsk, Yubileinoe, Sultanov), rhyolite–basalt (Yaman-Kasy, Blyava, Komosomol’sk, Sibai, Molodezhnoe, Valentorsk), and the less common serpentinite (Dergamysh) formations of the Urals (O–D2). In the ore-formational series of the massive sulfide deposits, probability of the detection of mineralized fauna correlates inversely with the relative abundance of felsic volcanic rocks underlying the ores. This series is also marked by a gradual disappearance of colloform pyrite, marcasite, isocubanite, pyrrhotite, and pyrite pseudomorphoses after pyrrhotite; increase of the amount of bornite, fahlores, and barite; decrease of contents of Se, Te, Co, and Sn in chalcopyrite and sphalerite; and decrease of Tl, As, Sb, and Pb in the colloform pyrite. Probability of the detection of mineralized fauna in the morphogenetic series of massive sulfide deposits decreases from the weakly degraded sulfide mounds to the clastic stratiform deposits. The degradation degree of sulfide mounds and fauna preservation correlates with the attenuation of volcanic intensity, which is reflected in the abundance of sedimentary and volcanosedimentary rocks and the depletion of effusive rocks in the geological sections.     

Massive sulfides of Mount Jourdanne along the super-slow spreading Southwest Indian Ridge and their genesis

Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.     

Tellurium-bearing minerals in zoned sulfide chimneys from Cu-Zn massive sulfide deposits of the Urals, Russia

Tellurium-bearing minerals are generally rare in chimney material from mafic and bimodal felsic volcanic hosted massive sulfide (VMS) deposits, but are abundant in chimneys of the Urals VMS deposits located within Silurian and Devonian bimodal mafic sequences. High physicochemical gradients during chimney growth result in a wide range of telluride and sulfoarsenide assemblages including a variety of Cu-Ag-Te-S and Ag-Pb-Bi-Te solid solution series and tellurium sulfosalts. A change in chimney types from Fe-Cu to Cu-Zn-Fe to Zn-Cu is accompanied by gradual replacement of abundant Fe-, Co, Bi-, and Pb- tellurides by Hg, Ag, Au-Ag telluride and galena-fahlore with native gold assemblages. Decreasing amounts of pyrite, both colloform and pseudomorphic after pyrrhotite, isocubanite ISS and chalcopyrite in the chimneys is coupled with increasing amounts of sphalerite, quatz, barite or talc contents. This trend represents a transition from low- to high sulphidation conditions, and it is observed across a range of the Urals deposits from bimodal mafic- to bimodal felsic-hosted types: Yaman-Kasy → Molodezhnoye → Uzelga → Valentorskoye → Oktyabrskoye → Alexandrinskoye → Tash-Tau → Jusa.     

Geochronological and isotopic constraints on Palaeoproterozoic skarn base metal mineralisation in the central Gawler Craton, South Australia

The mineralisation potential of Palaeoproterozoic strata from the central Gawler Craton, South Australia, is poorly known. This study defines the timing of Zn-rich skarn formation within Palaeoproterozoic calcsilicate and highlights this as a new mineralisation style for the Gawler Craton. Sulphides within the garnet–diopside skarn in the No. 17 Bore Prospect are predominantly in the form of sphalerite, associated with galena, minor chalcopyrite, pyrrhotite and pyrite. Sulphide is present in disseminated form and as a coarse-grained sulphide within a sericite-rich cavity-fill. Mineralisation is inferred to have formed at 1710 ± 16 Ma through a Sm–Nd isochron from garnet and diopside aliquots. A weakly mineralised and altered granite immediately below the calcsilicate skarn crystallised at 1729 ± 13 Ma (LA-ICPMS U–Pb zircon), within error of the skarn mineralisation. The skarn is interpreted to have formed through the initiation of fluid circulation as a result of high-level granite emplacement within the Palaeoproterozoic strata. Exploration for skarn Zn–Pb deposits such as the No. 17 Bore Prospect is assisted by their geophysical properties.     

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe₇S₈, and its absolute magnetic susceptibility is 2.10^− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (²⁰⁶Pb/²⁰⁴Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (²⁰⁶Pb/²⁰⁴Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO₂ conditions and neither a high temperature nor a low aH₂S (below 10^− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.     

Silver and silver-bearing minerals at the Um Samiuki volcanogenic massive sulphide deposit, Eastern Desert, Egypt

The Um Samiuki Zn–Cu–Pb–Ag mineralisation, south Eastern Desert, Egypt is hosted by felsic volcanic rocks which form part of the 712-Ma-old, east-west-trending Shadli Volcanic Belt. Two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the Western and Eastern mine areas. In each occurrence, a bornite-bearing zone is overlain by a pyrite-chalcopyrite-bearing zone and underlain by a disseminated, Cu-depleted zone. In the massive sulphide ore, sphalerite, chalcopyrite, pyrite, galena, bornite and tetrahedrite–tennantite are major minerals, whereas arsenopyrite, pyrrhotite, molybdenite and magnetite are accessory phases. Covellite and digenite are common secondary minerals. Bornite, tetrahedrite–tennantite and covellite contain high amounts of silver (averages of 1.97, 1.39 and 1.82 wt% respectively). Based on mineralogical balance calculations, bornite and covellite accommodate 80% of silver in the Um Samiuki deposit. Ag was incorporated in the crystal structure of the early-crystallised copper sulphides and sulphosalts and silver minerals. The temperature, sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver. Post-depositional deformation and metamorphic processes caused liberation, remobilisation and redeposition of silver within the massive sulphides.Editorial handling: D. Lentz     

Mineralogy and textures of the Lahanos and Kızılkaya massive sulphide deposits,northeastern Turkey,and their similarity to Kuroko ores

A distinct vertical zonation very similar to that described for the Kuroko deposits of Japan, is displayed by both mineralogy and textures of sulphides from the Lahanos and Kzlkaya massive sulphide deposits of northeastern Turkey. A deeper erosional level is exposed at the Kzlkaya deposit, so that only remnants of the massive sulphide ore zone are present. The zonation is from an upper zone of massive Cu and Zn sulphides (black and yellow ore) with fine-grained, colloform, banded, framboidal, and spherulitic textures, downwards through an intermediate zone of low Cu-Zn massive pyrite with transitional textures, to a lower zone of stockwork and impregnated pyrite displaying euhedral, zoned textures. The fine-grained and colloform pyrite of the upper zones is progressively overgrown by, and recrystallized to, the massive and euhedral pyrite of lower zones. The original textures of these deposits are best preserved by pyrite. The previous interpretation of these textures, of sulphide deposition from colloidal solutions ponded by an impermeable pyroclastic horizon, is reexamined in the light of present observations. Although ultra-fine-grained sulphides, framboids, and radially-cracked spherules could have formed by replacement of pre-existing minerals by a colloidal solution, the colloform and banded textures are indicative of growth in open spaces. It thus seems likely that the fine-grained colloform sulphides, including chalcopyrite, sphalerite, and tennantite as well as pyrite, were initially deposited on or near the surface of the sea-floor. Additional evidence for this interpretation is seen in the progressive recrystallization of the sulphide textures to massive, much coarser, pyrite in the lower zones. This recrystallization may in part be due to diagenetic and hydrothermal processes operating after formation of the original layered sulphides. These conclusions are in agreement with those reached for the similar, but larger Madenköy deposit 100 km to the east.     

The Daduhe gold field at the eastern margin of the Tibetan Plateau: He, Ar, S, O, and H isotopic data and their metallogenic implications

The Daduhe gold field comprises several shear-zone-controlled Tertiary lode gold deposits distributed at the eastern margin of the Tibetan Plateau. The deposits are hosted in a Precambrian granite–greenstone terrane within the Yangtze Craton. The gold mineralization occurs mainly as auriferous quartz veins with minor sulphide minerals. Fluid inclusions in pyrite have ³He/⁴He ratios of 0.16 to 0.86 R_a, whereas their ⁴⁰Ar/³⁶Ar ratios range from 298 to 3288, indicating a mixing of fluids of mantle and crust origins. The δ³⁴S values of pyrite are of 0.7–4.2‰ (n = 12), suggesting a mantle source or leaching from the mafic country rocks. δ¹⁸O values calculated from hydrothermal quartz are between − 1.5‰ and + 6.0‰ and δD values of the fluids in the fluid inclusions in quartz are − 39‰ and − 108‰. These ranges demonstrate a mixing of magmatic/metamorphic and meteoric fluids. The noble gas isotopic data, along with the stable isotopic data suggest that the ore-forming fluids have a dominantly crustal source with a significant mantle component.     

Significance of Late Devonian – Lower Carboniferous ages of hydrothermal sulphides and sericites from the Urals Volcanic-Hosted Massive Sulphide deposits

Formation of the Urals Volcanic-Hosted Massive Sulphide (VHMS) deposits is considered to be related with the intra-oceanic stage of the island arc(s) development in Late Ordovician – Middle Devonian time (ca. 460–385 Ma) based on the biostratigraphic record of ore-hosting sedimentary rocks. However, the known radiometric ages of ore hosting volcanics are very limited. Here we present direct dating results of sulphide mineralisation from the Yaman-Kasy and Kul-Yurt-Tau VHMS deposits using Re-Os isotope systematics showing similar mineralisation ages of 362 ± 9 Ma and 363 ± 1 Ma. These ages coincide with the previous Re-Os dating of the Alexandrinskoe (355 ± 15 Ma) and Dergamysh (366 ± 2 Ma) VHMS deposits. This Late Devonian (Famennian) age corresponds to the late stage of the ‘Magnitogorsk arc – Laurussia continent’ collision event and coincides with a beginning of large scale subduction-related granitoid magmatism. The younger mineralisation age relative to the biostratigraphic ages of host rocks is interpreted as one of the latest episodes of the multi-stage history of VHMS deposits development. Ar-Ar ages of sericites from metasomatic rocks of Barsuchi Log and Babaryk deposits show even younger ages clustering around 345 Ma, and testify another late hydrothermal event in the history of the Urals VHMS deposits.     

Heavy-mineral concentrates from rocks in exploration for massive sulphide deposits

A number of programs have investigated the use of rock geochemistry in the search for volcanogenic massive sulphide deposits in the Canadian Shield. Regional-scale studies have been successful in differentiating productive from nonproductive volcanic cycles. Wall-rock studies have successfully delineated alteration halos related to the mineralizing event. While an alteration halo has been identified around the South Bay massive sulphide deposit, this halo does not extend far enough from the deposit to be useful for reconnaissance purposes. The authors therefore tested the possibility of enhancing detection of a primary trace-element halo by using the heavy mineral fraction of the rocks.The geochemical dispersion of trace elements in the heavy-mineral fraction of rocks was investigated around the South Bay massive sulphide deposit, in the Superior Province of the Canadian Shield. Approximately 270 samples were ground to 74–500 μm (−35 +200 mesh) and separated using the heavy liquid bromoform. Following removal of the magnetic fraction, the samples were further pulverized, and analyzed by atomic absorption spectrophotometry for Cu, Pb, Zn, Ag, Fe, Mn, Co and Ni. Corresponding whole-rock samples were analyzed to provide for a comparative study with the whole-rock geochemistry.Analysis of the heavy-mineral fraction of rocks revealed strong and extensive halos of Cu, Pb, Zn and Ag persisting in some cases up to 10 km along strike away from the South Bay Deposit. By comparison, in the whole-rock data, halos of Pb, Ag and Zn were detected no farther than 1–2 km away from the deposit. Furthermore, trace-element content in the whole rocks appeared to be dominated by rock type; either multivariate statistical techniques, or separation of the data by rock type, was necessary to distinguish the anomaly related to mineralization. Trace-element content in the heavy-mineral concentrates was dominated by the presence of the sulphide minerals pyrite, chalcopyrite, and sphalerite, thus directly reflecting mineralization.Use of the heavy-mineral fraction of the rock eliminates the dilution effects of quartz and feldspar, allowing enhancement of trace-metal concentrations in sulphide minerals, and the delineation of strong and extensive halos of Cu, Pb, Zn, Ag and Mn around the South Bay massive sulphide deposit. While the cost of preparation of heavy-mineral separates is higher than that for whole-rock samples, the anomaly clearly defined by the trace-element content of the heavy fraction avoids the need for costly major-element and subsequent statistical analysis, and increases target size by an order of magnitude. The heavy-mineral fraction obtained from rocks shows great potential as an exploration guide to volcanogenic massive sulphide deposits.     

Characterization of the reactivity of riverine heterogeneous sediments using a facies-based approach; the Rhine–Meuse delta (The Netherlands)

Large groundwater resources are found in densely populated lowland areas, which consist often of young unconsolidated and reduced sediments. When anthropogenic activities lead to oxygenation of the aquifer, breakdown of the main reduced fractions, i.e. sedimentary organic matter (SOM) and pyrite, could lead to severe groundwater deterioration such as acidification, heavy metal mobilization, and increased hardness. The characterization of the reactive properties of these sediments is important in predicting groundwater deterioration, but is often complicated by the high degree of heterogeneity of these sediments. In this study, the potential reduction capacity (PRC, based on SOM and pyrite content), the potential buffer capacity (PBC, based on carbonate content), potential acidification capacity (PAC, based on the potential acid production by sulfide oxidation), and the measured reduction capacity (MRC) of five facies, which are typical of the riverine sediments in the Rhine–Meuse delta (The Netherlands) were determined. A universal facies-classification model was used to classify the deposits into more homogeneous sub-units based on lithologic and geogenic properties, with a further sub-division into oxic or anoxic redox environment based upon groundwater data and field observations. The bulk chemical data show strong variation across facies for the median values of PRC (186–9093 mmol O₂ kg⁻¹), PBC (17–132 mmol O₂ kg⁻¹), and PAC (36–1530 mmol H⁺ kg⁻¹). The MRC was measured as reactivity to molecular O₂ exposure and was 0.5–567.3 mmol O₂ kg⁻¹. Steady-state oxidation rates were in the wide range of 0.001–10.355 mmol O₂ kg⁻¹ day⁻¹ but were typically about 3–8 times faster in fine facies than in coarse facies. Both the PRC and MRC depend strongly on grain size, but also on the syn/post-depositional environment and redox conditions. The main part of the PRC consists of SOM, but pyrite reactivity is higher than SOM reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments. Some facies are very prone to acidification because the PAC is higher than the PBC, but the oxidation experiments also show that acidification could already start before the PRC is fully exhausted. This study, is one of the few that combines bulk chemical data, groundwater data, and reactivity measurements and shows that a facies-based approach is a practical tool in characterizing the reactivity of heterogeneous deposits.     

Erratum to: “Criteria for the detection of hydrothermal ecosystem faunas in ores of massive sulfide deposits in the Urals”

The ore-formational, ore-facies, lithological, and mineralogical-geochemical criteria are defined for the detection of hydrothermal ecosystem fauna in ores of the volcanic-hosted massive sulfide deposits in the Urals. Abundant mineralized microfauna is found mainly in massive sulfide mounds formed in the jasperous basalt (Buribai, Priorsk, Yubileinoe, Sultanov), rhyolite—basalt (Yaman-Kasy, Blyava, Komosomol’sk, Sibai, Molodezhnoe, Valentorsk), and the less common serpentinite (Dergamysh) formations of the Urals (O—D₂). In the ore-formational series of the massive sulfide deposits, probability of the detection of mineralized fauna correlates inversely with the relative abundance of felsic volcanic rocks underlying the ores. This series is also marked by a gradual disappearance of colloform pyrite, marcasite, isocubanite, pyrrhotite, and pyrite pseudomorphoses after pyrrhotite; increase of the amount of bornite, fahlores, and barite; decrease of contents of Se, Te, Co, and Sn in chalcopyrite and sphalerite; and inсrease of Tl, As, Sb, and Pb in the colloform pyrite. Probability of the detection of mineralized fauna in the morphogenetic series of massive sulfide deposits decreases from the weakly degraded sulfide mounds to the clastic stratiform deposits. The degradation degree of sulfide mounds and fauna preservation correlates with the attenuation of volcanic intensity, which is reflected in the abundance of sedimentary and volcanosedimentary rocks and the depletion of effusive rocks in the geological sections.     

Brine pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. I. Comparisons with the Iberian pyrite belt

The Ordovician Zn–Pb–Cu massive sulphide ore deposits of the Bathurst mining camp share many features with those of the Devonian/Carboniferous Iberian pyrite belt, particularly the tendency to large size (tonnage and metal content); shape, as far as can be determined after allowing for deformation; metal content, particularly Fe/Cu, Pb/Zn and Sn; mineral assemblages (pyrite + arsenopyrite ± pyrrhotite and lack or rarity of sulphates); sulphide textures (particularly framboidal pyrite); lack of chimney structures and rubble mounds; irregular metal or mineral zoning; and the low degree of zone refining compared to Hokuroku ores. The major differences between the provinces are the lack of vent complexes and the presence of Sn–Cu ores in the Iberian pyrite belt. There are also similarities in the geological setting of the two camps: both lie within continental terranes undergoing arc-continent and continent–continent collision, and in each case massive sulphide mineralisation followed ophiolite obduction; the ore deposits are associated with bimodal volcanic rocks derived from MORB and continental crust and marine shales; and mineralisation was locally accompanied or followed by deposition of iron formations.Fluid inclusion data from veins in stockworks from at least six of the Iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline, ore-forming fluids (brine pools), and it is suggested that most of the major features of the Bathurst deposits can be explained by similar processes. The proposed model is largely independent of ocean sulphate and O₂ content, whereas low values of each are requisites for the current, spreading-plume model of sulphide deposition in the Bathurst camp.     

Partition of cadmium and manganese between coexisting sphalerite and galena from some Japanese epithermal deposits

Sphalerites from Japanese epithermal Pb-Zn vein-type deposits, namely, Yatani, Oizumi and Hosokura, contain 2900–3400 ppm cadmium and 760–2100 ppm manganese. And galenas from the same deposits contain cadmium and manganese 19.2–26.9 ppm and 7.8–218.3 ppm, respectively. The temperatures, evaluated from the partition of cadmium between coexisting sphalerite and galena, are consistent within a total range of 150°C at maximum within an individual deposit. No systematic change with depth can be observed at the Shoko-hi vein, Hosokura mine and Hompi vein, Yatani mine. In several samples, the temperatures obtained from the partition of cadmium have been compared with those obtained from sulfur isotope fractionations. Iron content in sphalerite coexisting with pyrite indicates that the deposition of ore minerals at these deposits may have taken place from ore-forming solutions in which H₂S or HS^– was the predominant dissolved sulfur species, and the solutions may have been free from in situ oxidation or reduction.